1. Field of the Invention
This invention relates to processes for the preparation of photographic emulsions and more particularly to said processes wherein the photographic emulsion contains mixed crystal silver halide grains.
2. Description of the Prior Art
Various processes for the precipitation of silver halide grains are known in the art of preparing photographic emulsions, including double jet processes and stream processes which are described in The Theory of The Photographic Process, Third Edition, Mees-James, Macmillan Co., New York (1966) at 31 and 40 respectively. In the double-jet process, the silver nitrate solution and halide solution are simultaneously added to a mixing vessel containing a gelatin solution. In the stream process, the silver nitrate solution and halide solution are fed into a constant volume chamber wherein precipitation of all grains takes place in the same environment.
U.S. Pat. No. 3,415,650, issued to Frame, discloses a process wherein the silver nitrate and halide solutions are fed into a centrifugal mixing chamber submerged in a ripening vessel containing gelatin. The gelatin is drawn into the mixing chamber wherein precipitation of silver halide is accomplished within the confines of the mixing chamber and the silver grains are dispersed in the gelatin. The dispersion is forced through slots in the mixing chamber by centrifugal force into the ripening vessel.
British Pat. No. 1,243,356 discloses a similar process wherein the precipitation chamber is located outside the ripening chamber and at least some of the dispersion in the ripening chamber is recycled to the precipitation chamber.
The objectives of the various processes of the prior art generally include the preparation of reliable and reproducible emulsions at practical rates of throughput. The preparation of such emulsions, and the resulting quality of photographic film made therefrom, is highly dependent on the uniformity of the silver halide grains of the emulsions. Indeed, even with careful ingredient selection, maintaining a photographic environment, and the most skillful subsequent tailoring of the emulsions, significant film quality variations can result from irreproducibilities in the precipitation and ripening steps of the emulsion preparation. Accordingly, it is the object of the present invention to provide a process for preparing a photographic emulsion having silver halide grains of controlled grain size, structure and size distribution.